1. Field of the Invention
The present invention relates to compositions and methods for making microporous materials made of nonoxide ceramics.
2. Description of the Related Art
Various microporous ceramic materials are used as a filter, a catalyst carrier, a substrate of a separation membrane used as a gas separating member or the like.
In recent years, nonoxide ceramics having silicon such as silicon nitride and silicon carbide as the main constituent gain attention as a microporous ceramic material used for these applications. For example, the microporous ceramic materials having silicon nitride as the main constituent have excellent heat resistance and thermal shock resistance, and are suitable for use under a high temperature environment (300° C. or more, for example, 600° C. or more and less than 1000° C.).
Japanese Laid-Open Patent Publication No. 8-133857 describes a microporous ceramic material comprising silicon nitride which is used under a high temperature environment as a gas or liquid filter or a catalyst carrier and a method for making the same.
Conventionally, the microporous nonoxide ceramic materials used for the above-listed applications are made in the following manner (see the above-mentioned Laid-Open Publication): a powder of the nonoxide ceramic (e.g., silicon nitride powder) is used as the raw material, and the powder was molded into a predetermined shape and sintered. However, the nonoxide ceramic powder such as silicon nitride is expensive, compared with common oxide ceramic powders (e.g., silica powder, alumina powder). For this reason, the nonoxide ceramic materials such as silicon nitride obtained by sintering such a nonoxide ceramic powder are more expensive than oxide ceramic materials.
It is an object of the present invention to provide a microporous ceramic material made of nonoxide ceramics having silicon as the main constituent element in a lower cost of the raw material and more inexpensively than conventional microporous ceramic materials, in particular, to provide a microporous ceramic material suitable for use as a filter, a catalyst carrier, a support of a separation membrane (gas separation membrane or the like).